1. Field of the Invention
This invention relates to ammunition for use in a weapon having a rifled barrel, and especially to an improved form of projectile for small arms ammunition.
2. Discussion of Prior Art
When a projectile is fired from a rifled barrel, the projectile must deform as it travels along the barrel so that material forming part of the projectile is forced into the spaces between the lands forming the rifling. This process is called engraving, and causes a spin to be imparted to the projectile by virtue of the longitudinal twist of the rifling.
The deformation of the projectile, its travel along the barrel effectively as a force fit to the rifling, the high linear acceleration imparted by the gun propellant on firing, and the consequent high rate of angular acceleration and associated force acting between rifling and projectile all contribute to substantial wear on the barrel.
If this wear rate can be reduced, substantial benefits follow, including increased barrel life, higher muzzle velocity and hence increased accuracy and lethality.
For this reason, low friction, readily deformable materials are normally selected for small arms bullets, for example lead. In order to increase the overall density of the bullet, it has also been proposed to use steel. However, steel is not readily deformable, and causes unacceptable barrel wear. On the other hand, hardness is a very desirable characteristic for the bullet material, in order to minimise nose tip ablation during penetration of hardened targets such as, for example, titanium/kevlar body armour. For these purposes, a Vickers Hardness of at least 550 (using a 10 kg load) is the minimum desirable.
In seeking to overcome these problems, it has been common practice to make a small arms bullet from a steel core, enclosed in a gilding metal jacket.
This latter solution is practical, but results in a bullet having a relatively expensive construction. This is a very significant disadvantage since small arms ammunition is consumed in large quantities, and the market for such ammunition is highly competitive.
In U.S. Pat. No. 5,686,693 there is disclosed a 7.62 mm bullet formed from a steel alloy, having a forward body portion whose diameter corresponds to that of the rifling lands of an associated gun, and a rearward body portion having a greater diameter, and provided with annular grooves. The body is provided with a coating which can be of copper. In use, the copper coating acts as a lubricant, and is less thick than the depth of the rifling. When fired from the rifled barrel, the rifling therefore cuts through the copper coating so that the steel body of the bullet is engraved by the rifling. In the disclosure it is stressed that the steel of the body must be soft, so as to permit this engraving to occur without undue barrel wear. The maximum value for the hardness of the steel body mentioned in the disclosure is 210 Brinell, which equates to a Vickers Hardness of 213, i.e. very much less than the desirable minimum value of 550 Vickers Hardness. As a result, the bullet disclosed in U.S. Pat. No. 5,686,693 will lack the desirable hardened target penetration capability.
It would therefore be a considerable advantage if a way could be found to utilise steel or other metal having a Vickers Hardness equal to at least 550 (using a 10 kg load) as the principal component of a small arms projectile, while enabling the projectile to be engraved by the rifling and not introducing unacceptable friction or wear, and avoiding the expensive construction of applying a jacket to the projectile.